The copper ETN’s rise has brought it close to $50 a share, which has been a key level in recent years. A rally earlier this year failed near $50, while a break below $50 in 2008 forecasted the big slide.

A break-out in copper would be an encouraging sign for the global economy, and Goldman Sachs is bullish. Goldman analysts on Tuesday raised their copper price forecasts. “We still favor copper and believe that shortages will lead to price spikes in 2011,” they wrote in a note.